In order to being able to boot the LFS system, we need to update our bootloader. We're assuming that your host system is using Lilo (since that's the most commonly used boot loader at the moment).
We will not be running the lilo program inside chroot. Running lilo inside chroot can have fatal side-effects which render your MBR useles and you'd need a boot disk to be able to start any Linux system (either the host system or the LFS system).
First we'll exit chroot and copy the lfskernel file to the host system:
logout
cp $LFS/boot/lfskernel /boot
The next step is adding an entry to /etc/lilo.conf so that we can choose LFS when booting the computer:
cat >> /etc/lilo.conf << "EOF"
image=/boot/lfskernel
label=lfs
root=<partition>
read-only
EOF
<partition> must be replaced by the LFS partition's designation.
Now the boot loader gets updated by running:
/sbin/lilo
The last step is syncing the host system lilo config. files with the LFS system:
cp /etc/lilo.conf $LFS/etc &&
cp <kernel images> $LFS/boot
To find out which kernel images files are being used, look at the /etc/lilo.conf file and find the lines starting with image=. If your host system has kernel files in other places than the /boot directory, make sure you update the paths in the $LFS/etc/lilo.conf file so that it does look for them in the /boot directory.
As soon as we have booted into LFS we can run /sbin/lilo from the LFS system in order to have the latest Lilo version in the MBR.